Methods for producing enhanced interference pigments

ABSTRACT

Methods and apparatus are provided for uniformly depositing a coating material from a vaporization source onto a powdered substrate material to form a thin coalescence film of the coating material that smoothly replicates the surface microstructure of the substrate material. The coating material is uniformly deposited on the substrate material to form optical interference pigment particles. The thin film enhances the hiding power and color gamut of the substrate material. Physical vapor deposition process are used for depositing the film on the substrate material. The apparatus and systems employed in forming the coated particles utilize vibrating bed coaters, vibrating conveyor coaters, or coating towers. These allow the powdered substrate material to be uniformly exposed to the coating material vapor during the coating process.

CROSS-REFERENCE TO RELATED

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/539,695, filed Mar. 31, 2000, and entitled “Methods forProducing Enhanced Interference Pigments” and claims the benefitthereof.

BACKGROUND OF THE INVENTION

[0002] 1. The Field of the Invention

[0003] The present invention is related generally to thin film opticalcoatings for producing interference pigments. More specifically, thepresent invention is related to methods and apparatus for producing thininterference coatings in the form of thin coalescence films on pigmentparticles which exhibit enhanced colorant effects and hiding power.

[0004] 2. The Relevant Technology

[0005] Interference pigments and colorants have been used to provide acolored gloss in substances such as cosmetics, inks, coating materials,ornaments and ceramics. Typically, a silicatic material such as mica,talc or glass is coated with a material of high refractive index, suchas a metal oxide, and a layer of metal particles is further deposited ontop of such highly refractive material. Depending on the type and thecontent of the highly refractive material, different types of gloss andrefractive colors are produced.

[0006] Thin film flakes having a preselected single color have beenpreviously produced. For example, U.S. Pat. No. 4,434,010 disclosesflakes composed of symmetrical layers that may be used in applicationssuch as automotive paints and the like. The flakes are formed bydepositing a semi-opaque metal layer upon a flexible web, followed by adielectric layer, a metal reflecting layer, another dielectric layer,and finally another semi-opaque metal layer. The thin film layers arespecifically ordered in a symmetric fashion such that the same intendedcolor is achieved regardless of whether the flakes have one or the otherlateral face directed towards the incident radiation.

[0007] High chroma interference platelets for use in paints, includingcolor shifting and nonshifting single color platelets, are disclosed inU.S. Pat. No. 5,571,624. These platelets are formed from a symmetricalmultilayer thin film structure in which a first semi-opaque layer suchas chromium is formed on a substrate, with a first dielectric layerformed on the first semi-opaque layer. An opaque reflecting metal layersuch as aluminum is formed on the first dielectric layer, followed by asecond dielectric layer of the same material and thickness as the firstdielectric layer. A second semi-opaque layer of the same material andthickness as the first semi-opaque layer is formed on the seconddielectric layer. For the color shifting designs, the dielectricmaterials utilized, such as magnesium fluoride, have an index ofrefraction less than 2.0. For small shifting or nonshifting designs, thedielectric materials typically have an index of refraction greater than2.0.

[0008] U.S. Pat. No. 5,116,664 discloses a pigment that is made bycoating a first layer of TiO₂ onto mica followed by coating the TiO₂layer with powder particles of at least one of the metals cobalt,nickel, copper, zinc, tin, gold, and silver. The metallic powder layeris deposited by an electroless wet chemical process to a thickness of 5to 1000. Electron micrographs showed that these particles were in theform of finely divided rods.

[0009] U.S. Pat. No. 5,573,584 discloses a process for preparing forgeryproof documents by printing with interference pigments. The pigments areformed by overcoating platelet-like silicatic substrates (micas, talc orglass flakes) with a first colorless or selectively absorbing metaloxide layer of high refractive index, a second non-selectively absorbingsemitransparent layer, and optionally, a third layer comprising acolorless or selectively absorbing metal oxide in combination withscattering pigments. The second non-selectively absorbingsemitransparent layer may be composed of carbon, a metal, or a metaloxide, which, for example, can be applied by gas phase decomposition ofvolatile compounds, such as compounds of iron, cobalt, nickel, chromium,molybdenum or tungsten, or metal oxides such as iron oxide, magnetite,nickel oxide, cobalt oxides, vanadium oxides, or mixtures thereof.

[0010] Overcoating of a base material such as a TiO₂-coated silicaticsubstrate with an outer layer of carbon, metal or metal oxide is usuallyaccomplished in conventional processes by chemical deposition methodssuch as electroless plating or pyrolysis methods. Electroless platingmethods involve a redox process with no extraction or supply of electriccurrent. Pyrolysis methods rely on the thermal decomposition of avolatile compound such as a hydrocarbon or an organometallic compoundwhose pyrolytic decomposition product is deposited on the surface to becoated.

[0011] Electroless deposition methods and pyrolytic methods, however,produce large islands or dots of the material being deposited on thebase material. Consequently, continuous coating is obtained at theexpense of depositing enough coating material to sufficiently coat thegaps between such large islands or dots. This extensive deposition leadsin turn to a thick coating which, because of its thickness, does notgenerate the best chromatic colors. In short, these conventional methodsproduce thick coalescence layers.

[0012] When the preservation of the surface structure of the materialthat is being coated is desired, a thick coalescence layer has thedisadvantageous feature of significantly altering such underlyingsurface structure. For example, photomicrographs of TiO₂-coated micathat were treated in an electroless cobalt plating bath have beenreported as showing finely divided rod-like particles on the surface ofthe TiO₂ layer. See, for example, U.S. Pat. No. 5,116,664, FIG. 1 andcol. 6, lines 10-16, showing and describing a coating with finelydivided rod-like particles.

[0013] Chemical methods of deposition and electroless plating methodsare typically limited to materials that involve hydrocarbons (liquid orgases), to organometallic compounds, and to metals, such as silver ornickel, that can readily be deposited by electroless processes. It isdesirable, however, to manufacture mica interference pigments withmethods that permit a much wider choice of materials. In particular, itis desirable to develop a process that can utilize materials, such asmetals and sub-oxides, that can be vacuum deposited, materials, such asmetal carbides, metal nitrides, metaloxynitrides, metal borides, andmetal sub-oxides, that can reactively be deposited in vacuum, andmaterials, such as diamond-like carbon and amorphous carbon, that can bedeposited by plasma-assisted vacuum methods.

[0014] Chemical methods of deposition and electroless plating methodstypically generate solutions that must be disposed of, and some of thesemethods rely on catalytic substances that are incorporated into thepigments to an extent such that it prevents the use of the pigment incertain applications in various consumer products such as cosmetics. Toavoid these problems and limitations, it is desirable to developprocesses for manufacturing pigments that are more environmentallyfriendly and that do not rely on materials that can limit the use of thepigments. In particular, it is desirable to develop processes thatreduce or eliminate the use of toxic materials and hazardous methods ofdeposition.

[0015] In addition to the need for developing processes formanufacturing interference pigments that can use a great variety ofmaterials, it is also desirable to develop processes that can usecheaper materials and that permit the production of highly adherent andhard films that do not easily detach themselves from the substrate. Inparticular, it is desirable to provide processes that use materialsother than the relatively expensive and mostly toxic metal carbonylsthat typically require an investment in equipment for handling them andfor monitoring their use in specially confined facilities.

SUMMARY AND OBJECTS OF THE INVENTION

[0016] It is a primary object of the invention to provide methods andapparatus for the production of thin interference coatings in the formof thin coalescence films on inorganic particles to form a pigmentcomposition.

[0017] It is also an object of the invention to form thin coalescencefilms which replicate the surface microstructure of the underlyingsubstrate particles without forming islands, rod-like or otheragglomerates in the coating that would structurally alter the underlyingsubstrate surface microstructure.

[0018] It is another object of the invention to provide pigmentcompositions that exhibit enhanced color effects and hiding power.

[0019] To achieve the foregoing objects, and in accordance with theinvention as embodied and broadly described herein, methods andapparatus are provided for uniformly depositing a coating material froma vaporization source onto a powdered substrate material to form a thincoalescence layer of the coating material that smoothly replicates thesurface microstructure of the substrate material. This is accomplishedin a dry vacuum deposition process and in the absence of liquidsolutions to form a powdered pigment composition.

[0020] In particular, uniform deposition of the coating material isachieved by directing an inorganic powdered substrate material into avacuum chamber containing a coating material vaporization source, andgenerating a coating material vapor from the coating materialvaporization source in a dry vacuum process. The powdered substratematerial is exposed to the coating material vapor in a substantiallyuniform manner, and a thin coalescence film of one or more layers of acoating material is formed on the powdered substrate material thatsubstantially replicates a surface microstructure of the powderedsubstrate material. The apparatus and systems employed in forming thecoated particles utilize vibrating bed coaters, vibrating conveyorcoaters, coating towers, and the like. These allow the powderedsubstrate material to be uniformly exposed to the coating material vaporduring the coating process.

[0021] A pigment composition produced by the method of the inventionincludes a powdered substrate material comprising a plurality ofinorganic core particles having an observable surface microstructure. Acoalescence film substantially surrounds the core particles of thesubstrate material, and the coalescence film substantially replicatesthe surface microstructure of the core particles. The pigmentcomposition can be combined with various pigment media in order toproduce a colorant composition for use in paints, inks, or plastics. Inaddition, the pigment particles can be optionally blended with otherpigment flakes, particles, or dyes of different hues, chroma andbrightness to achieve the color characteristics desired.

[0022] The pigment compositions of the present invention exhibitenhanced hiding power, enhanced chroma on a white background andenhanced selected chromas on a black background. These pigmentcompositions also exhibit a greater available color gamut. The hardnessand good adherence exhibited by the coalescence films on the pigmentparticles lead to advantages such as durability and the absence ofrub-off coating losses.

[0023] These and other objects, features, and advantages of the presentinvention will become more fully apparent from the following descriptionand appended claims, or may be learned by the practice of the inventionas set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to illustrate the manner in which the above-recited andother advantages and objects of the invention are obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings in which:

[0025]FIG. 1 shows a schematic cross-sectional view of an embodiment ofthe coating apparatus of the invention that has a vibrating bed;

[0026]FIG. 2 shows a schematic cross-sectional view of an embodiment ofthe coating apparatus of the invention that has a rotating drum coater;

[0027]FIG. 3A shows a schematic perspective view of an embodiment of thecoating apparatus of the invention that has an electromagnetic conveyorcoater;

[0028]FIG. 3B shows a side view of the electromagnetic conveyor coaterthat is part of the embodiment shown in FIG. 3A;

[0029]FIG. 3C shows a top view of the embodiment shown in FIG. 3A;

[0030]FIG. 4A shows a schematic cross-sectional view of an embodiment ofthe coating apparatus of the invention that has a free-fall tower;

[0031]FIG. 4B shows a square arrangement of coating materialvaporization sources;

[0032]FIG. 4C shows a hexagonal arrangement of coating materialvaporization sources;

[0033]FIG. 5A shows a schematic cross-sectional view of an embodiment ofthe coating apparatus of the invention that has an oblique tower;

[0034]FIG. 5B shows a cross-sectional view of the device shown in FIG.5A in a plane that is orthogonal to the longitudinal axis of theembodiment shown in FIG. 5A;

[0035]FIG. 6A is a scanning electron microscopic picture at 50000× ofthe surface of Gold Pearl pigment prior to Cr-deposition according tothe invention;

[0036]FIG. 6B is a scanning electron microscopic picture at 50000× ofthe surface of Cr-coated Gold Pearl pigment according to the invention;

[0037]FIG. 7A is a scanning electron microscopic picture at 75000× ofthe surface of Super Green Pearl pigment prior to Cr-depositionaccording to the invention;

[0038]FIG. 7B is a scanning electron microscopic picture at 75000× ofthe surface of Cr-coated Super Green Pearl pigment according to theinvention;

[0039]FIG. 7C is a scanning electron microscopic picture at 100000× ofthe surface of Cr-coated Super Green Pearl pigment according to theinvention;

[0040]FIG. 8 is a plot in a*b* color space showing the hue and chromachanges for three pigments upon Cr-coating according to the invention;

[0041]FIG. 9 is a plot in a*b* color space of color coordinates for thepigment Violet Pearl on two background materials upon Cr-coatingaccording to the invention;

[0042]FIG. 10 is a plot in a*b* color space of color coordinates for thepigment Gold Pearl on two background materials upon Cr-coating accordingto the invention;

[0043]FIG. 11 is a plot in a*b* color space of color coordinates for thepigment Super Green Pearl on two background materials upon Cr-coatingaccording to the invention;

[0044]FIG. 12 is a plot in a*b* color space of color coordinates for thepigment Super Red Mearlin Luster on two background materials uponCr-coating according to the invention;

[0045]FIG. 13 is a plot in a*b* color space of color coordinates for thepigment Merck Iriodin® 221 Blue on two background materials uponCr-coating according to the invention;

[0046]FIG. 14 is a plot in a*b* color space of color coordinates for thepigment Irioding 289 Flash Interference Blue on two background materialsupon Cr-coating according to the invention; and

[0047]FIG. 15 is a plot in a*b* color space of color coordinates for thepigment Iriodin® 299 Flash Interference Green on two backgroundmaterials upon Cr-coating according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0048] The present invention is directed to methods and apparatus forcoating a powdered substrate material to produce optical interferencepigment compositions with enhanced colorant effects. The methods andapparatus provide for uniform deposition of a coating material from avaporization source onto a powdered substrate material to form a thincoalescence film of the coating material. The thin coalescence filmenhances the hiding power and color gamut of the pigment composition.

[0049] As discussed in greater detail below, physical vapor depositionprocesses are used for depositing a coating material to form a thincoalescence film on the powdered substrate material. The apparatusemployed in forming the coated particles utilize vibrating bed coaters,vibrating conveyor coaters, coating towers, or the like. These allow thepowdered substrate material to be uniformly exposed to the coatingmaterial vapor during the coating process. A coating materialvaporization source used in the deposition process can be selected froman evaporative source, a sputtering source, an electron beam depositionsource, an arc vapor deposition source, and the like.

Pigment Composition

[0050] The pigment composition produced by the methods and apparatus ofthe invention includes a powdered substrate material comprising aplurality of inorganic core particles having an observable surfacemicrostructure. A thin coalescence film substantially surrounds the coreparticles of the substrate material such that the coalescence filmsubstantially replicates the surface microstructure of the coreparticles. The coated particles of the pigment composition generallyhave a single-layered or multi-layered interior structure, with a thincontinuous layer of the coalescence film substantially surrounding eachof the particles. The pigment composition can be combined with variouspigment media in order to produce a colorant composition for use inpaints, inks, or plastics. The colorant composition produces apredetermined optical response through radiation incident on a surfacecoated with the colorant composition. The optical response includesenhanced color effects that are due to the coating deposited on thesubstrate material according to this invention.

[0051] The substrate material can be selected from a variety ofparticulate materials such as various silicatic materials. Othersuitable substrate materials include multilayer platelets such asMgF₂/Al/MgF₂ platelets, SiO₂/Al/SiO₂ platelets, andsolgel-SiO₂/Al/SiO₂-solgel platelets, interference glass flakes (i.e.,glass flakes having a defined thickness in the range from about 0.2 μmto about 1 μm), and combinations thereof. The MgF₂, SiO₂, andsolgel-SiO₂ layers on the aluminum cores of the above platelets can havean optical thickness ranging from about 2 quarter waves (qw) at about400 nm to about 8 qw at about 700 nm. The substrate material can be aparticulate material, such as mica flakes, glass flakes, talc, boronnitride, and the like, which can be used uncoated, or precoated with ahigh refractive index material. The high refractive index material ispreferably a dielectric material with an index of refraction of greaterthan about 1.65. Examples of suitable high refractive index dielectricmaterials include titanium dioxide, zirconium oxide, tin oxide, ironoxide, zinc oxide, tantalum pentoxide, magnesium oxide, tungstentrioxide, carbon, and combinations thereof. One preferred substratematerial is a TiO₂-coated silicatic material such as TiO₂-coatedinterference mica. The substrate materials described herein can be usedsingly or in a variety of combinations as desired.

[0052] A variety of coating materials can be used to form the thincoalescence film on the substrate particles according to the presentinvention. For example, the coating material can include various lightabsorbing materials. Suitable coating materials include metals,sub-oxides such as metal sub-oxides, oxides including metal oxides,nitrides such as metal nitrides and metaloxynitrides, borides such asmetal borides, carbides, sulfides, carbon such as diamond-like carbonand other amorphous carbon (e.g., poco, graphite or vitreous) materials.Preferred coating materials include gray metals and compounds thereofsuch as chromium, titanium, palladium, tin, nickel, cobalt, as well asother materials such as silicon, carbon, copper, and aluminum. Variouscombinations of any of the above coating materials may also be utilized.More generally, coating material choice in this invention includes anymaterial that can be vacuum-deposited, reactively deposited in vacuum,or deposited in plasma assisted vacuum processes.

[0053] An absorber coating composed of a multilayer structure of two ormore layers can also be used. For example, in the chamber shown in FIGS.3A-3C (discussed in detail hereinafter), using alternate targets ofdifferent materials, an alloy or a material composed of extremely thinlayers can be deposited. In the case of an alloy, the alloy may formspontaneously or may simply be indistinguishable from a multilayeredabsorber layer since the coating thickness for each layer can be on theorder of about 5 Angstroms or less, and even less than about 1 Angstrom.As the substrate particles travel around the vibrating trays in thechamber, the particles are coated by a thin deposition from each sputtertarget. The particles not only experience movement under the target, butare agitated under each target as well by a particular vibrating tray.

[0054] Combinations of different absorber coating materials such asTi/C, Pd/C, Zr/C, Nb/C, Al/C, Cu/C, TiW, TiNb, Ti/Si, Al/Si, Pd/Cu,Co/Ni, Cr/Ni, and the like, can be utilized to form a multilayercoating. These different material combinations can each be depositedsequentially as alternating layers on the substrate particles so thatthe coalescent film on the particles is composed of multiple layers oftwo different absorber materials. Preferably, the different materialsused together in the coating each have a refractive index (n) and anabsorption coefficient (k) that are approximately equal. Alternatively,three different coating materials can be employed, or as many differentmaterials can be used as there are targets. Alloys can also be used ineach target for the coating, such as titanium silicide (TiSi₂),Hastelloys (e.g., Ni—Mo—Fe, Ni—Mo—Fe—Cr, Ni—Si—Cu), Monels (e.g.,Ni—Cu), Inconels (e.g., Ni—Cr—Fe), Nichromes (e.g., Ni—Cr), and variousstainless steels. Details regarding the properties of these and otheralloys can be found in the Chemical Engineers' Handbook, McGraw-Hill,2nd Ed., 2116 (1941), the disclosure of which is incorporated byreference herein.

[0055] One preferred embodiment of a coating material includesalternating layers of titanium and carbon (Ti/C) formed on particles ofa substrate material such as TiO₂-coated interference mica. The titaniumlayers are separated by the carbon layers and each particle isencapsulated with a final thin layer of carbon. The titanium and carbonlayers are sequentially deposited from different targets at a thicknessto provide absorbing properties to the coating material. The number oflayers deposited depends on the thickness of the layers. For example, alarger number of layers are formed for the coating material when each ofthe layers are a few angstroms thick, whereas fewer layers are formedwhen each of the layers are many angstroms thick. Each of the layers oftitanium and carbon can have a thickness ranging from about 1 Å to about50 Å. Another preferred coating of alternating layers includes titaniumand silicon (Ti/Si), which can be formed in a similar manner as the Ti/Ccoating discussed above.

[0056] The sub-oxides prepared in the vacuum process are depositedeither by directly evaporating the sub-oxide (e.g., TiO_(x), wherex=1-1.9) or by reactively evaporating the metal in the presence of pureoxygen, moisture or air. The carbides are deposited by reactiveevaporation of metals with hydrocarbon gas, such as methane. Borides aredeposited by evaporation of metals in the presence of diborane orhalogenated borides, such as BF₃ (g). Nitrides are deposited in thepresence of nitrogen gas, and oxynitrides are deposited in the presenceof gas mixtures, such as oxygen/nitrogen mixtures, air/nitrogenmixtures, and water vapor/nitrogen mixtures. Ammonia may be substitutedfor the nitrogen if desired. Alternating layers of a metal and a nitrideor oxynitride can be formed as the coating material such astitanium/titanium nitride, or titanium/titanium oxynitride.

[0057] The coating material is preferably deposited on the substrateparticles so as to form a thin coalescence film having a thickness fromabout 30 Å to about 150 Å, and preferably a thickness from about 60 Å toabout 100 Å. The exact thickness, however, depends strongly on theoptical properties of the absorbing material.

[0058] The pigment composition of the invention can be combined withvarious pigment media such as acrylic melamine, urethanes, polyesters,vinyl resins, acrylates, methyl methacrylate, ABS resins, epoxies,styrenes, ink and paint formulations based on alkyd resins, and mixturesthereof. The pigment composition combined with the pigment mediaproduces a colorant composition that can be used directly as a paint,ink, or moldable plastic material. The colorant composition can also beutilized as an additive to conventional paint, ink, or plasticmaterials.

[0059] In addition, the pigment composition can be optionally blendedwith various additive materials such as conventional pigment flakes,particles, or dyes of different hues, chroma and brightness to achievethe color characteristics desired. For example, the pigment compositioncan be mixed with other conventional pigments, either of theinterference type or noninterference type, to produce a range of othercolors. This preblended composition can then be dispersed into apolymeric medium such as a paint, ink, plastic or other polymericpigment vehicle for use in a conventional manner.

[0060] Examples of suitable additive materials that can be combined withthe coated particles of the invention include non-color shifting highchroma or high reflective platelets which produce unique color effects,such as MgF₂/Al/MgF₂ platelets or SiO₂/Al/SiO₂ platelets. Other suitableadditives that can be mixed with the pigment composition of theinvention include lamellar pigments such as aluminum flakes, graphiteflakes, glass flakes, iron oxide, boron nitride, mica flakes,interference based TiO₂ coated mica flakes, interference pigments basedon multiple coated platelike silicatic substrates, metal-dielectric orall dielectric interference pigments, and the like; and non-lamellarpigments such as aluminum powder, carbon black, ultramarine blue, cobaltbased pigments, organic pigments or dyes, rutile or spinel basedinorganic pigments, naturally occurring pigments, inorganic pigmentssuch as titanium dioxide, talc, china clay, and the like; as well asvarious mixtures thereof. For example, pigments such as aluminum powderor carbon black can be added to control lightness and other colorproperties.

[0061] The pigment composition of the invention can be easily andeconomically utilized in paints and inks for various applications toobjects and papers, such as motorized vehicles, currency and securitydocuments, household appliances, architectural structures, flooring,fabrics, sporting goods, electronic packaging/housing, toys, productpackaging, etc. The pigment composition can also be utilized in formingcolored plastic materials, coating compositions, extrusions,electrostatic coatings, glass, and ceramic materials.

Vapor Deposition Methods

[0062] To produce coatings in the form of thin coalescence layers, theinvention relies on dry, physical vapor deposition methods and vacuumdeposition sources. The deposition methods produce very finedistributions of nucleation sites on the surface of the material to becoated, and in particular, the deposition methods utilized producecoalescence layers thin enough so as to minimally or negligibly alterthe structural features of the underlaying material surfacemicrostructure. The thin coalescence layers that can be obtained withsuch fine nucleation site distributions lead to comparatively thinnercoatings, with better chromatic colors.

[0063] In physical vapor deposition methods, the material to bedeposited has to be initially evaporated and deposition is subsequentlyaccomplished by depositing the evaporated material on a selectedsubstrate. The low temperature vapor deposition methods utilized in thepresent invention are all physical vapor deposition methods and includeresistive evaporation, electron beam deposition, cathodic arcevaporation, carbon rod arc evaporation, magnetron sputtering includingboth planar and hollow cathode, balanced and unbalanced sputtering, aswell as radio frequency sputtering.

[0064] In resistive evaporation the material is brought to theevaporation temperature with the aid of a resistance source in anevaporative source. Typically, an element made of a metal such astungsten, tantalum or molybdenum holds the material to be evaporated andis heated by passing an intense electric current through the element.

[0065] In electron beam deposition the material is heated by bombardmentwith high energy electrons until the material evaporates. This techniquehas the ability to concentrate a large amount of power in a smallsurface and it thus provides temperatures that are higher than themelting and evaporation points of refractory oxides and even refractorymetals used in resistive evaporation.

[0066] Arc vapor deposition uses a high intensity current, low voltagearc to vaporize a cathodic electrode (cathodic arc) or anodic electrode(anodic arc) and deposit the vaporized material on a substrate. Arcvaporization, especially cathodic arc evaporation, provides copiousamounts of film-ions and reactive gas ions.

[0067] The carbon rod arc evaporation differs from the above describedcathodic arc evaporation in that the former operates in direct current(DC) mode while the latter operates in alternating current (AC) mode.The carbon rods are forced together to form an electrical short whichcauses high carbon temperature in the contact area, and thereforeevaporation.

[0068] Sputtering is ejection by bombardment and sputter deposition is anon-thermal process where the atoms of the material to be evaporated areejected upon energetic collision with impinging particles that aretypically inert gaseous ions and more particularly argon cations. Theinert gas ions are formed by ionizing collisions with electrons in avacuum chamber and they are accelerated by an electric potential towardsthe material to be sputtered. The material that is evaporated bysputtering subsequently deposits on a substrate.

[0069] According to a basic sputtering technique, a sputtering cathodeand an anode are enclosed in a chamber that contains rarefied inert gas.These electrodes are connected to a high voltage DC power supply whichaccelerates electrons to the anode. Electrons collide with the inert gasto form inert gas anions that accelerate to the cathode. The anionscollide with the sputtering cathode material and vaporize the materialthat is subsequently deposited on a substrate interposed between thesputtering cathode and the anode. This is DC sputtering or moreprecisely DC diode cathodic sputtering, which typically operates atpressures in the order of 10-2 Torr.

[0070] The ion formation rate in a sputtering chamber can be enhanced byproviding electrons from, for example, a source such as a heatedfilament. The electrons are accelerated by a discharge DC power supply.This enhancement in the electron generation rate leads to an increase inthe deposition rate, and systems that operate according to thisprinciple are known as triode sputtering systems.

[0071] A sputtering system that, instead of a high voltage DC powersupply, has a radio frequency (RF) power supply and a matching chamberis a RF sputtering system. This system prevents the charge build-up in anonconducting material that is to be sputtered and it consequentlypermits the sputtering of insulating materials, typically beingperformed at pressures of an order of magnitude as low as 10⁻⁴ Torr.

[0072] Deposition rates achieved with radio frequency sputtering systemscan be further increased with magnetron sputtering. As in the previouslyintroduced sputtering techniques, a plasma exists in the sputteringchamber of a magnetron sputtering device, but appropriately generatedmagnetic fields additionally force the electrons to follow paths in theregion near the sputtering cathode. Accordingly, the frequency ofcollisions with inert gas atoms is higher and more sputtering ions areformed. The progressive increase in sputtering and deposition rates isalso characterized by a correspondingly increased ability to perform thedeposition at lower pressures.

[0073] In ion beam sputtering an ion source provides a focused,divergent or collimated ion beam. The ion beam, in the form of a beamplasma, is directed against a sputtering target and the sputtered atomsare deposited on a substrate.

[0074] Reactive sputtering is a sputtering process in which a gas isintroduced into the chamber so it reacts with the evaporated material toform a compound that is deposited on the substrate. Even when a compoundis sputtered directly, the addition of a reactive gas may be necessaryto compensate for the dissociation losses of the reactive component.

[0075] Although reactive sputtering can arguably be classified as achemical vapor deposition method, reactive methods used in thisinvention rely on vacuum deposition sources that are used in physicalvapor deposition methods. In this sense, the reactive deposition methodsof this invention are referred to in this context as physical vapordeposition methods.

[0076] Sputtering can be carried out by using “balanced” or “unbalanced”magnetic field confinement. “Balanced” magnetron or “standard”sputtering occurs when most of the magnetic field lines are confined tothe target region. Unbalanced sputtering occurs when an externalmagnetic field is placed behind the substrate, or the magnets behind thesputtered target are of different strengths so that the ion and electronflux extends out away from the target toward the substrate. Generally,unbalanced magnetron sputtering rates are higher than for “balanced”magnetron sputtering with higher ion fluxes. Higher fluxes modify thegrowing deposited film to produce such changes as harder films withdiffering optical properties. A good review of the difference between“balanced” and “unbalanced” magnetron sputtering can be found in thefollowing references which are incorporated herein by reference in theirentirety: B. Window and N. Savvides, J. Vac. Sci. Technol. Vol. A4(2)196 (1986); and N. Savvides and B. Window, J. Vac. Sci. Technol. Vol.A4(3) 504 (1986).

[0077] Sources of electrons that are used for heating and ionizing atomsand molecules include hot electron emitting surfaces and plasma sources.In plasma sources, electrons are magnetically deflected from a plasma.In particular, the hollow cathode electron source uses a plasmadischarge in a cavity that reflects and traps electrons.

[0078] These and other deposition techniques have been described in R.Herrmann and G. Bräuer, DC and RF-Magnetron Sputtering, and J. Becker,Ion Beam Sputtering, in Handbook of Optical Properties, vol. 1, pp.135-212, R. E. Hummel and K. H. Guenter (eds.), CRC Press (1995), whichare incorporated by reference herein in their entirety.

[0079] In alternating current magnetron sputtering, e.g., “dualmagnetron sputtering”, the voltage between two sputter sources isalternated to facilitate the continuous sputtering of conductors thatdevelop insulating layers in reactive sputtering. In this mode ofdeposition, a reactive gas such as oxygen, nitrogen, methane, andethylene is introduced near the substrate surface in addition to thenoble working gas (e.g., argon). By alternating the targets betweencathodic and anodic charge, both targets remain free of insulatingreactants.

[0080] The MetaMode™ process developed by Optical Coating Laboratory,Inc., (U.S. Pat. Nos. 4,851,095 and 5,225,057, which are incorporatedherein by reference in their entirety), allows continuous sputtering ofa metallic target where a reactive process takes place in anothercontiguous chamber. Such a process is useful in making TiO_(x) orSiO_(x) absorbing layers from Ti metal or Si metal depositions.

[0081] The use of an ion gun to bombard the surface of the growingabsorber film with ions is applicable to this invention since many filmsneed hardening to prevent the outer layer from abrading off duringmilling of the pigment or application (compounding in plastics orpainting) to the final product. In addition charge build-up on thepowders during deposition could be reduced by the application of suchions. Various means to coat such powders by ion assisted processesinclude ion plating, and reactive ion plating and are well known tothose skilled in the art.

Vapor Deposition Systems and Apparatus

[0082] The coating apparatus of this invention includes a substrateexposure device. The substrate exposure device is configured such thatthe substrate particles are uniformly exposed to the coating materialduring the coating process. An exemplary embodiment of a substrateexposure device is a vibrating bed that has a sample receptacle, such asa pan, that is connected to a vibrating device, such as a toroidalelectromagnetic vibrator. Additional exemplary embodiments of substrateexposure devices are vibrating conveyors, rotating drum coaters,oscillatory drum coaters, and free-fall chambers.

[0083] In some embodiments of this invention, the substrate exposuredevice is located within a rarefied chamber (hereinafter referred to as“vacuum chamber”). For example, the vibrating beds, vibrating conveyors(e.g., electromagnetic or pulsating gas-driven devices), rotating drumcoaters and oscillatory drum coaters are located within a vacuumchamber. In other embodiments of this invention, the substrate exposuredevice itself serves as the chamber whose interior is subject torarefaction during deposition. For example, “waterfall-equipped”chambers and free-fall chambers are embodiments of substrate exposuredevices that serve themselves as vacuum chambers.

[0084] In embodiments of the substrate exposure device of thisinvention, the particles of the substrate material are exposed to avacuum deposition source, such as a hollow cathode sputtering system ora DC magnetron sputtering system. For example, a DC magnetron sputtertarget of chromium was used to deposit a uniform layer of chromium overthe surfaces of interference mica. Visual inspection revealed that theappearance of the particles went from a pale white to a visual color,and turned gray with further deposition, gray being the color ofelemental chromium. Too much chromium coating resulted in the depositionlayer being too thick and the coating was opaque. As long as thechromium layer was still semi-opaque (partially transmitting), enhancedcolor could be achieved as well as higher hiding. When the substrate wassubject to vibration while being exposed in an embodiment of thesubstrate exposure device, the pigment could be significantly improvedin color by adjusting the degree of vibration, the time of deposition,the power to the sputter target, the throw distance, and the amount ofsubstrate pigment being coated.

[0085] In addition to a substrate exposure device, embodiments of thecoating apparatus of this invention also have a vacuum deposition sourceas a coating material vaporization source. Exemplary configurations ofthese elements are illustrated by the embodiments disclosed hereinbelow.

[0086] Any of the embodiments of the coating apparatus of this inventionherein disclosed provides effective and uniform exposure of thesubstrate material powder. This means that statistically all the sidesof the substrate material powder particles are approximately equallyexposed to the coating material that is to be deposited on them. Thistype of exposure is hereinafter referred to as “uniform exposure”.

[0087]FIG. 1 schematically shows a vertical cross-sectional view of acoating apparatus 100 according to one embodiment of the invention, inwhich a vacuum chamber 110 encloses a coating material vaporizationsource 120 and the substrate exposure device that is embodied by avibrating bed 130. A powdered substrate material 132, such asTiO₂-coated mica, is placed in a rotatable container 134, which isoperatively connected to a vibrator 140. In one embodiment, container134 is located on and attached to a base 135 by a conventional fastener136. In other embodiments, base 135 is integrally attached to container134, or base 135 forms the base of container 134 itself. Container 134is more particularly embodied by any receptacle that can effectivelyhold substrate material 132 while it is being coated, such as abowl-shaped container, a dish or a pan.

[0088] The vibrator 140 comprises a vacuum sealed electromagnet 142. Inthis embodiment, base 135 is made of a magnetic material, preferablymagnetic steel. Furthermore, flat springs 144 connect base 135 with thebottom of electromagnet 142 or with a fixed surface 146 so that base 135is prevented from contact engagement with electromagnet 142, and base135 can move without experiencing collisions against any other part ofelectromagnet 142. During operation of coating apparatus 100, substratematerial 132 undergoes a substantially helical motion that isrepresented in FIG. 1 by arrows A1 and A2. This continuous mixing ofsubstrate material 132 in container 134 provides for a good statisticaldistribution of the thickness of the deposited coating on the substratematerial.

[0089] The coating material is vaporized from coating materialvaporization source 120, which in one embodiment of this invention is anevaporative source. In other embodiments of this invention coatingmaterial vaporization source 120 is a magnetron sputtering unit or anyof the vacuum deposition sources described hereinabove. As depicted inFIG. 1, a flow 152 of vaporized coating material emanates from coatingmaterial vaporization source 120 to reach and coat substrate material132.

[0090] When electromagnet 142 was operated in the approximate voltagerange of 0-50 V at 60 Hz, it generated an alternating magnetic fieldthat successively attracted and released base 135 at a frequency of 60Hz, thus causing partially circular up-and-down oscillations ofbowl-shaped container 134. When electromagnet 142 was turned on, analternating magnetic field attracted base 135 to the top ofelectromagnet 142 and released it with the frequency of 60 Hz. Flatsprings 144 did not let base 135 contact the top of electromagnet 142and returned base 135 to the original position every time when the fieldchanged its polarity. With these oscillations imparted to container 134,substrate material 132 was continuously mixed and effectively anduniformly exposed to the vaporized material that deposited on thesurface of the particles of substrate material 132.

[0091] The appropriately rarefied environment in the chamber wheredeposition takes place in the embodiment schematically shown in FIG. 1or in any other embodiment disclosed hereinbelow is achieved with theaid of conventional vacuum pumping systems. These systems typicallyinclude a cryopump, a diffusion pump coupled to a mechanical pump orother suitable vacuum pump, or combinations thereof, with the suitablevacuum lines and exhaust ports. These systems are known to those skilledin vacuum technology and are not further discussed here.

[0092] In preferred embodiments, the size of the vibrator bowl can rangefrom 4 inches to about one foot in diameter. The vibrator should be soconstructed that little outgassing occurs from its components, andpreferably, stainless steel is used in its construction. Embodiments ofcoating material vaporization source 120 (also referred to as sputteringtarget or simply target) may be any shape including annular orrectangular. A preferred embodiment for chromium deposition comprises awater cooled DC magnetron with a chromium target having dimensions of 12inches by 4.4 inches by 0.50 inches thick. Annular targets having radiifrom about 4-9 inches could be used as well as larger rectangulartargets up to about 11 inches by about 4 feet long. By using multiplecathodes arranged in a square with multiple vibrating bowls, largevolumes (about 5 pounds) of pigment can be produced in one batchoperation. In an embodiment with a small 4-inch radius vibrator bowl andone overhead coating material vaporization source, about 10 grams ofpigment could be effectively processed.

[0093]FIG. 2 schematically shows a vertical cross-sectional view of acoating apparatus 200 according to another embodiment of the invention,in which a vacuum chamber 210 encloses a coating material vaporizationsource 220 and the substrate exposure device that is embodied by arotating drum coater 230. A substrate material 232, such as TiO₂-coatedmica, is placed in a hollow drum 233 which is rotated as indicated, forexample, by arrow A3 under the power delivered at a chosen angularfrequency by a shaft 234. The interior wall 235 of drum 233 is somanufactured as to provide for the effective mixing and uniform exposureof substrate material 232.

[0094] A plurality of ledges 238 extend generally inwards from interiorwall 235 of drum 233 so that, upon revolving drum 233, ledges 238 lift acertain amount of the powder of substrate material 232. As drum 233continues turning, the powder of substrate material 232 falls backdownwards thus undergoing the efficient mixing that leads to uniformexposure and subsequent deposition of coating material. The ledges 238are arranged so that the powder of substrate material 232 preferablyfalls back in such a way that most of the powder is effectively exposedto the flow of coating material. For example, in the arrangementdepicted in FIG. 2, this is accomplished by forcing the powder to fallback shortly after each ledge has passed the relevant equatorial zone ofthe drum, forcing the powder to undergo a motion schematically indicatedby arrow A4. The ledges 238 are arranged differently in otherconfigurations so as to provide the desired uniform exposure of thepowder of substrate material 232 depending on how and where coatingmaterial vaporization source 220 is located within vacuum chamber 210.Furthermore, other features that accomplish an equivalent result can beused instead of ledges 238, such as flanges, bars, paddles, and blades.

[0095] The coating material is vaporized form coating materialvaporization source 220, which in one embodiment of this invention is aphysical evaporative source. In other embodiments of this inventioncoating material vaporization source 220 is a magnetron sputtering unitor any of the vacuum deposition sources described hereinabove. Asdepicted in FIG. 2, a flow 252 of vaporized coating material emanatesfrom coating material vaporization source 220 to coat substrate material232.

[0096] The drum coater 230 is a preferred exemplary embodiment of acoater of this invention that is in other embodiments shaped like agenerally rotary cylindrical coater, or in general like a rotarycontainer that is suited for mixing the powder of substrate material 232and exposing it to vaporized coating material.

[0097] The rotating drum coater has been described previously. Teer, inReactive Magnetron Sputter Barrel Ion Plating, as reported in ConferenceProceedings IPAT 91, pp. 303-308, Brussels, Belgium, which isincorporated herein by reference in its entirety, shows a typical drumor barrel coater in FIGS. 1-3 which has a diameter of about 2 feet.However, there are physical constraints in making a bigger chamber, suchas a chamber 6 feet in diameter. The two-foot chamber used was equippedwith a sputtering system in which the deposition occurred downward onpowder flowing across the bottom inside of the rotating drum. Theinterior of the barrel was provided with angled bars which allowed thepigment to be agitated uniformly and not lost to the ends of the barrel.

[0098]FIG. 3A schematically shows a perspective view of a coatingapparatus 300 according to a further embodiment of the invention, inwhich a vacuum chamber 310 encloses both a coating material vaporizationsource 320 and the substrate exposure device, which is embodied by avibrating conveyor coater 330. As shown in FIG. 3A, vibrating conveyorcoater 330 preferably has four conveyors 371, 372, 373, and 374 whichare disposed so that the powder of a substrate material 332 effectivelycirculates counterclockwise as indicated by arrows A5. While the powdercirculates along this path, it is effectively mixed so that its exposureto the vaporized coating material is uniform. Efficient mixing alsooccurs at the end of each conveyor as the powder drops in a waterfalloff of one tray and onto the next. The vaporized coating material isprovided by coating material vaporization source 320, which in oneembodiment of this invention is a physical evaporative source. In otherembodiments of this invention coating material vaporization source 320is a magnetron sputtering unit or any of the vacuum deposition sourcesdescribed hereinabove.

[0099] A vibrating means is provided to force the powder of thesubstrate material 332 to circulate. For example, in one embodiment,vibrating conveyor coater 330 can be associated with a plurality ofelectromagnets 342 which act as the vibrating means. FIG. 3Bschematically shows a side view of conveyor coater 330, and inparticular, the components of the electromagnetic conveyors whichinclude a tray 334, a shaft 335, an electromagnet 342, and a spring 344.The tray 334 can be made of a variety of materials, and preferably ismade of stainless steel. As indicated in FIG. 3B, tray 334 islongitudinally tilted with respect to the horizontal plane by an anglethat is preferably between about 1° and about 20° , and more preferablybetween about 1° and about 5°. In this arrangement, electromagnet 342 islocated near a lower end 337 of tray 334 and preferably under such lowerend. A higher end 339 of tray 334 is preferably cut as shown in FIG. 3C,preferably at an angle of about 45° with respect to the longitudinalaxis of tray 334. One end of spring 344 is preferably attached toelectromagnet 342 and its opposite end is attached at a point near lowerend 337 of tray 334. Similarly, one end of shaft 335 is attached toelectromagnet 342 and the opposite end is attached preferably to aregion under tray 334 that is located between the half-length point oftray 334 and lower end 337. Furthermore, shaft 335 is conventionallyattached to electromagnet 342 to effectively force tray 334 to oscillateaccording to corresponding oscillations generated by electromagnet 342.The restoring effect of spring 344 effectively creates a torque thattends to restore tray 334 to the position that it had prior to thedisplacement caused by electromagnet 342 acting upon shaft 335. Theoverall dynamic behavior of tray 334 coupled with spring 344 and shaft335 is such that the powder of substrate material 332 is effectivelyforced upwards from lower end 337 to higher end 339 along tray 334.

[0100] In other embodiments of the vibrating conveyor coater of thepresent invention, the vibrating tray can be energized by othervibrating means such as a pulsating gas-driven device. For example, apulsating air piston known as a pneumatic drive, attached to thevibrating tray, can be used to induce the vibrating motion in the tray.Such pneumatic drive systems are available from Martin Engineering(Livonia, MI).

[0101] Each one of trays 334 in the embodiment schematically shown inFIG. 3A is disposed so that each higher end 339 is located above lowerend 337 of the next tray along the overall circulation path of substratematerial 332. This arrangement is shown in the perspective view of FIG.3A and in the side view of FIG. 3B. When conveyor coater 330 has fourconveyors, they are disposed with respect to each other in the abovedescribed configuration at preferably about 90° angles, as shown in theperspective view of FIG. 3A and in the top view of FIG. 3C.

[0102]FIG. 3B shows tray 334 lengthwise and also shows an end view ofthe following tray, electromagnet and spring in the sense of circulationof substrate material 332. Primed and unprimed numbers in FIG. 3B labelanalogous elements in the lengthwise view and in the end view,respectively.

[0103]FIG. 3C shows a top view of the embodiment shown in FIG. 3A, wheredifferently shaded areas represent different trays 334 of differentconveyors 371-374 forming a closed-loop square array. As schematicallyshown in FIG. 3C, the powder of substrate material 332 is forced to moveby the vibration of tray 334 along conveyor 371, and is coated with thevaporized coating material from coating material vaporization source320. The coated powder then drops off at the higher end 339 of conveyor371 onto lower end 337 of conveyor 372. Consequently, the powder movesalong the path indicated by arrows A5. The overall powder flow changestravel direction by approximately 90° when it is dropped from oneconveyor to the next conveyor along the path. In addition, the powderfalls several inches when it is delivered from one conveyor to thefollowing conveyor so that the powder is thoroughly mixed to provideuniform exposure to the vapor of the coating material that is to depositon and coat substrate material 332. The approximately 45° cut at thehigher end 339 of each tray 334 permits a uniform fall of the powderonto the entire width of the lower end 337 of the following tray.

[0104] The counterclockwise overall circulation of substrate material332 as shown in FIGS. 3A and 3C is merely illustrative of one possiblecirculation in an embodiment of this invention. Modifications to thedevices shown in FIGS. 3A, 3B and 3C could be made by one of ordinaryskill in the art to produce another embodiment of this invention inwhich the overall circulation of substrate material 332 is clockwise.

[0105] In a typical embodiment of the vibrating conveyor coater, traydimensions are about 28 inches long by about 7 inches wide, althoughcommercially available conveyors come in lengths up to 30 feet andwidths up to 2 feet. Multiple two-foot wide sputter targets would allowdeposition through the length of the larger vibrating trays. Instead ofa square arrangement, embodiments of this device could have triangulartray arrangements, pentagonal arrangements, hexagonal arrangements, orarrangements in some other shape. Still another embodiment of thisdevice could have a long vibrating tray with multiple overheadevaporating sources. Vibrating conveyors of this type are available fromARBO Engineering (North York, Ontario, Canada) and Eriez (Erie, Pa.).The preferred arrangement is the square arrangement of vibrating trayswith four waterfalls at each 90° turn.

[0106]FIG. 4A schematically shows a vertical cut-away view of a coatingapparatus 400 according to another embodiment of the invention, in whichthe vacuum chamber comprises a tall and narrow elongated coating towerstructure such as a free-fall tower 405 with a series of mounted coatingmaterial vaporization sources 420 and a container 450 for a substratematerial 432. The tower 405 is provided with a receptacle 434 to collectand facilitate the subsequent retrieval of a coated substrate material433.

[0107] In one embodiment of coating apparatus 400, coating materialvaporization sources 420 are magnetrons. In another embodiment, coatingmaterial vaporization sources 420 are hollow cathode sputtering systems.

[0108] When magnetrons are utilized for vaporization sources 420, themagnetrons can be mounted in a variety of configurations, but preferablythey are mounted in a square or hexagonal configuration, as shown inFIGS. 4B and 4C. These figures schematically illustrate cross-sectionalviews of coating apparatus 400 taken in a plane that is orthogonal tothe tower's longitudinal axis. FIG. 4B shows a cross-sectional view of asquare tower 406 with four magnetrons 421. FIG. 4C shows an analogouscross-sectional view of a hexagonal tower 407 with six magnetrons 422.Square and hexagonal shaded regions 425 and 426 schematically illustratethe region into which the plasma in towers 406 and 407, respectively, isconfined by the magnetic fields of the corresponding magnetrons 421 and422. In general, magnetrons are preferably installed over all sides ofthe coating tower to increase the deposition rate of the coatingmaterial onto the powder particles of substrate material 432.

[0109] The container 450 is provided with a mechanism for appropriatelyreleasing substrate material 432 into tower 405. In the embodimentillustrated in FIG. 4A, this mechanism is exemplary embodied by apercussion mechanism such as a hammer 452 that, as indicated by doublearrow A6, forces the release of substrate material 432 by appropriatelyshaking container 450. This can also be achieved by any other mechanismthat produces a similar effect, such as a vibrator.

[0110] As schematically shown in FIG. 4A, after substrate material 432has been released from container 450, substrate material 432 falls downthrough a series of plasma regions 427 and past coating materialvaporization sources 420. Because of convection and plasma forces, thepowder particles spiral down to the bottom where they are collected inreceptacle 434. The movement of the powder particles during fall allowsfor uniform exposure and deposition of a coating material thereon.

[0111]FIG. 5A schematically shows a vertical cross-sectional view of acoating apparatus 500 according to an additional embodiment of theinvention, in which the vacuum chamber comprises a tall and narrowoblique coating tower 505 with a series of mounted coating materialvaporization sources 520 and a container 550 for a substrate material532. The tower 505 is provided with a receptacle 534 to collect andfacilitate the subsequent retrieval of a coated substrate material 533.In one embodiment, coating material vaporization sources 520 aremagnetrons.

[0112] The tower 505 stands at an angle preferably in the range of about70°-89° relative to a horizontal plane intersecting the longitudinalaxis of tower 505. Equivalently, tower 505 stands at an angle preferablyin the range of about 1°-20° relative to a vertical axis, as shown inFIG. 5A.

[0113] Coating material vaporization sources 520, such as magnetrons,are mounted on one wall of tower 505. Within tower 505, a device isgenerally disposed along the wall opposite vaporization sources 520 toforce particles of substrate material 532 to undergo a motion such thatit renders them fully and uniformly exposed to the coating material thatemanates from vaporization sources 520. In one embodiment, this deviceis a vibrating tray 508 with ledges that is longitudinally disposedalong the wall opposite vaporization sources 520. In another embodiment,this device is a stationary tray with ledges that is generally disposedas tray 508.

[0114]FIG. 5B schematically shows a cross-sectional view of coatingapparatus 500 in a plane that is orthogonal to the longitudinal axis. Asshown in FIG. 5B, tray 508 is provided with longitudinally extendinglateral flanges 509 that confine the particles as they run downward overthe ledges of tray 508.

[0115] During operation of coating apparatus 500, a mechanism such as avibrator or a similar device forces substrate material 532 to bereleased from container 550 and to fall down on tray 508. Particles ofsubstrate material 532 slide along the ledges of tray 508, flipping andmixing, and pass through a series of plasma regions 527. The particlesare uniformly exposed and coated with the coating material that emanatesfrom coating material vaporization sources 520, resulting in coatedsubstrate material 533 which is collected in receptacle 534.

[0116] Preferred embodiments of the towers schematically shown in FIGS.4A and 5A are typically about 3 feet in diameter and about 6 feet long.These embodiments also include (not shown in FIGS. 4A-5A) a returnmechanism to the top of the tower for further processing of the pigment,if necessary. The pigment is circulated through the tower as many timesas necessary until the desired color is achieved. The return mechanismcan be embodied by a screw conveyor, a spiral vibrating elevator, or bya ferris wheel arrangement to reload the powder at container 450 or 550from the respective receptacle 434 or 534. The sputter targets are ofsuitable dimensions to fit within the chambers.

[0117] Elements of the embodiments of the coating apparatus of thisinvention described hereinabove, equivalents thereof, and theirfunctionalities can be expressed as means for performing specifiedfunctions as described hereinbelow.

[0118] Examples of means for directing an inorganic powdered substratematerial into a vacuum chamber include any of a variety of conventionalconveying devices known to those skilled in the art of vacuum depositionprocessing.

[0119] Examples of means for generating a coating material vapor includeany one of a plurality of coating material vaporization sources such assputtering sources including sputter magnetrons, hollow cathodesputtering systems, triode sputtering systems, RF sputtering systems,ion beam sputtering sources, hollow cathode sputtering systems, andreactive sputtering sources; evaporative sources; electron beamdeposition sources, and arc vapor deposition sources including cathodicarc vapor deposition sources and anodic arc vapor deposition sources, aswell as carbon rod arc evaporation.

[0120] Examples of means for uniformly exposing powdered substratematerial include any of a plurality of substrate exposure devices thatuniformly expose substrate material powder in a rarefied environment tocoating material vapor, such as vibrating beds and conveyors, rotatingdrum coaters, electromagnetic conveyor coaters, and coating towersincluding straight and oblique towers.

[0121] Examples of a means for providing a rarefied environment forvapor deposition include any one of a variety of vacuum pumping systemsincluding cryopumps, other vacuum pumps and combinations thereof, withthe appropriate vacuum lines and exhaust ports.

[0122] Feeding mechanisms such as a container coupled to a percussiondevice or to a vibrator are examples of means for supplying powderedsubstrate material. These mechanisms and equivalents thereof supplypowder substrate material to means for uniformly exposing substratematerial powder. Containing devices such as a receptacle are examples ofmeans for collecting coated substrate material powder. Feedingmechanisms and equivalents thereof, and containing devices andequivalents thereof are appropriately placed so that they do notinterfere with the uniform exposure of the substrate material powder tothe coating material vapor, so that they do not impede the deposition ofthe coating material vapor onto the substrate material powder, and sothat the rarefied conditions in which the vapor deposition takes placeare preserved.

Thin Coalescence Layer Coatings

[0123] The structure of the coated particles of the pigment compositionof the invention, particularly when the coating material is a metal, ismarkedly different from the structure of the pigments produced accordingto conventional methods. Electroless deposition and pyrolyticdecomposition methods for organometallic compounds produce large islandsor dots of metal. If these deposition methods are prolonged to induce acontinuous coating, the absorber coating becomes too thick atcoalescence to produce the best chromatic colors. In contrast, thephysical vapor deposition processes of this invention produce a veryfine distribution of nucleation sites on the surface of the substratematerial, such as the surface of TiO₂-coated mica, which in turn producea very thin coalescence thickness.

[0124] In this invention, the coating is not composed of dot-like orrod-like formations, and the continuous covering is achieved at a muchthinner coverage than with other methods, such as electroless orchemical vapor deposition processes. Metals and other materialsdeposited by physical vacuum processes according to the invention canhave a thickness of about 30-150 Å, and coalesce at thicknesses that areas small as about 30-50 Å. For example, a coalescence thickness of about40 Å was commonly achieved in the experiments performed in the contextof this invention.

[0125] Deposition according to this invention is supplemented in someembodiments with a process for altering the chemical makeup of thedeposited material. In one embodiment of this invention, the depositedmaterial is oxidized, forming a somewhat thicker layer that increasesthe durability of the final pigment. For example, the pigment productcan be baked after vacuum deposition to produce a thicker oxide layer,since a metal layer would be oxidized somewhat after the heatingprocess. The thickness of the layers of deposited material that areobtained in this way can be up to about 200 Å while still replicatingthe underlying structure of the material on which deposition takesplace.

[0126] In addition to the structural and optical properties of thecoatings produced with the apparatus, systems and methods of thisinvention, the dry processes of this invention are more environmentallyfriendly and comparatively less hazardous than conventional techniquesbecause the processes of this invention do not produce waste solutionsthat must be disposed of following the coating processes. In addition,the methods of this invention do not require the incorporation ofcatalytic ions such as palladium or tin ions that are necessary elementsin electrochemical wet chemical methods. The use of such ions maydisadvantageously prevent the subsequent use of the manufacturedpigments in various consumer products.

[0127] Furthermore, the methods and systems of this invention require nohigh heating or any pyrolysis. Instead, the coating is depositedaccording to the methods of this invention by a dry, low temperatureprocess rather than a wet chemical process or a pyrolytic process. Moreprecisely, “dry” in the context of this invention stands for thenon-reliance on solutions by the deposition methods. Instead, the dryvacuum methods of this invention are implemented under conditions thatare typical of physical vapor deposition techniques. The dry vacuumprocess of the invention can be carried out at a temperature of lessthan about 200° C. if desired. In one preferred method, the dry vacuumprocess is carried out at a near ambient temperature (e.g., about 20-60C). Alternatively, the dry vacuum process can be carried out at atemperature of about 200° C. or greater.

[0128] The coatings deposited according to this invention are highlyadherent, hard films that do not rub-off, unlike prior coatings such ascarbon coatings that are deposited by pyrolytic processes.Organometallic compounds are more expensive than the materials used inphysical deposition methods, and some of these compounds are toxic, aproperty that requires investment in equipment for handling thecompounds themselves and for monitoring the processes in which they areused.

Color Measurement

[0129] The chromatic properties of the coated particles producedaccording to the invention are quantitatively described with referenceto color measurement standards that are briefly summarized as follows.

[0130] In order to quantify the perceived color of a particular object,it is useful to invoke the XYZ tristimulus color coordinate systemdeveloped by the Commission Internationale de I'Éclairage (CIE), whichis now used as a standard in the industry in order to precisely describecolor values. In this system, colors can be related completely andaccurately through the variables X, Y, and Z, which are determinedmathematically as the integrals of three distribution functions coveringthe visible spectrum, which ranges from about 380 nm to about 770 μm,with the reflectance or transmittance curve and the energy distributionof the light source. The variables x, y, and z, which are normalizedvalues of X, Y, and Z, respectively, are known in the art as thechromaticity coordinates, and are routinely used in the industry toquantify aspects of color such as purity, hue, and brightness.

[0131] Another color coordinate system developed by CIE defines colorcharacteristics which account for the dependence of color sensitivity ofthe eye on viewing angle in terms of X₁₀Y₁₀Z₁₀ tristimulus values. Thesevalues may be used for viewing angles greater than 4° (and are exact fora viewing angle of 10°), while the values X, Y, and Z are reserved forviewing angles specified for a 4° angle or less.

[0132] The parameters X, Y, and Z are defined by the followingequations:

X=KS( )x′( )R( )d

Y=KS( )y′( )R( )d

Z=KS( )z′( )R( )d

[0133] where K=100/(S( )y′( )d)

[0134] S( ) is the relative spectral power distribution of theilluminant;

[0135] x′( ), y′( ), and z′( ) are the color matching functions for aspecified angle; and

[0136] R( ) is the spectral reflectance of the specimen.

[0137] The chromaticity coordinates, x, y, and z can be calculated fromthe X, Y, Z tristimulus values through the following formulae:

x=X/(X+Y+Z)

y=Y/(X+Y+Z)

z=Z/(X+Y+Z)=1−x−y.

[0138] From the x, y, z chromaticity coordinates, a useful diagram knownas the “chromaticity diagram” can be plotted, wherein the loci of x andy values correspond to all real colors; which in conjunction with thehuman eye response function and the third dimension of brightness (whichmay be conveniently plotted on an axis perpendicular to the chromaticityplane), can be used to completely describe all aspects of perceivedcolor. This system of color description is particularly useful when aquantitative comparison of color attributes is required.

[0139] The chromaticity plane may be described in a variety of ways;however, a standard in the industry is known as the L*a*b* color spacedefined by CIE (hereinafter referred to as the “CIELab space”). In thiscolor space, L* indicates lightness and a* and b* are the chromaticitycoordinates. In an L*a*b* chromaticity diagram, the a* axis isperpendicular to the b* axis, with increasingly positive values of a*signifying deepening chroma of red and increasingly negative values ofa* signify deepening chroma of green. Along the b* axis, increasinglypositive values of b* signify deepening chroma of yellow, whereasincreasingly negative values of b* indicate deepening chroma of blue.The L* axis indicating lightness is perpendicular to the plane of the a*and b* axes. Colors with no chroma always have the value a*=b*=0. The L*axis along with the a* and b* axes provide for a complete description ofthe color attributes of an object.

[0140] The L*a*b*color system allows for a comparison of the colordifferences between two measurements through a metric, namely E, whichindicates the change in color as measured in the L*a*b* color space. Thenumerical value for E is calculated through the following equation usingthe measured L*a*b* values:

E=[(L*)²+(a*)²+(b*)²]^(1/2)

[0141] where the symbol denotes a difference in measurements taken, forexample, at two different angles (e.g., 0° incidence and 45° incidence),or a difference in measurements taken for a reference standard and asample.

[0142] In general, three items are needed to specify our perception of agiven beam of light. The L*a*b* set of coordinates is one of such setsof three items. Another set incorporates lightness, L*, but instead ofthe coordinates a* and b*, it uses the coordinates C* and h, that standfor chroma and hue, respectively. Chroma measures color saturation.Increasing fading corresponds to lower saturation. Hue corresponds withthe dominant saturated color.

[0143] Color differences can also be expressed as a function ofdifferences in lightness, chroma and hue by the expression:

E=[(L*)²+(C*)²+(H*)²]^(1/2),

[0144] where C* stands for chroma and H* for change in metric hue. Themetric hue, h, is defined by

h=arctan (b*/a*)

[0145] and the chroma, C*, is defined by

C*=[a* ² +b* ²]^(1/2).

[0146] The widely used CIELab color space is adequate for describingpigments of a single color. However, color-shifting pigments such aslight interference pigments represent a significant challenge in colormeasurement. To quantify the dramatic hue shift and chroma of thesecolorants, metrologists at Flex Products, Inc., developed a new colormeasurement metric known as Dynamic Color Area™ (hereinafter “DCA™”).See Flex Products Technical Bulletin No. TB-02-98, which is herebyincorporated by reference herein in its entirety. Measurements tocompute the DCA™ metric are taken at a viewing geometry known as nearspecular multi-angle geometry, where the aspecular view angle is fixedrelative to the corresponding specular angle. The fixed aspecular angleis maintained at all selected angles of illumination. It is measuredusing a goniospectrophotometer, which is an instrument that allows forthe configuration of nearly 300 distinct measurement geometries. Inaddition, the DCA™ metric can also be applied to other multi-anglemeasurement geometries. Calculating the DCA™ metric under two differentgeometries allows for a comparison of pigment appearance under twosimulated viewing environments.

[0147] To generate the DCA™ diagram using the aspecular angle geometry,a series of readings are taken with a goniospectrophotometer at anglesfrom 10° to 60° incidence in 5° increments. These readings are plottedin a CIELab color space. Lines are drawn connecting the plot points andconnecting the 10° and 60° measurements to the achromatic point (a*=0,b*=0), thus defining a function f(a*, b*). The DCA™ metric isrepresented by the area in the a*-b* plane defined by the function f(a*,b*). The larger the area defined by the DCA™ metric for a given pigment,the larger that pigment's color gamut.

[0148] More explicitly, the DCA™ metric is described as a definedsurface integral

[0149] f(a*, b*) db* da* where the integrations are performed betweenthe lower and upper limits b₁, b₂, respectively, for b*, and the lowerand upper limits a₁, a₂, respectively, for a*. This double integralprovides an area in the a*-b* plane of the CIELab space. This area, andthus the DCA™ metric, is measured in square CIE units.

[0150] Experiments in the context of this invention were performed withcommercially available TiO₂-coated interference mica. The TiO₂-coatedmica having the colors of Super Green Pearl, Violet Pearl and Gold Pearlunder the tradename MasterTint® was obtained from DuPont. TiO₂-coatedmica under the tradename Iriodin® was also obtained from E. Merck(Darmstadt, Germany). Samples of Iriodin® 221 Blue, Iriodin® 289 FlashInterference Blue, and Iriodin® 299 Flash Interference Green were used.A sample under the Mearlin tradename labelled Super Red Mearlin Lusterpigment was obtained from the Engelhard Corporation (Ossining, N.Y.).Similar interference mica can be obtained from Kemira Oy (Pori,Finland), under the tradename Flonac. The substrate material was placedin a coating apparatus according to this invention, for example, avibrating bed in a vacuum chamber. Other experiments used a rotating oran oscillatory drum coater, electromagnetic conveyors, or free fallingcoating towers.

EXAMPLES

[0151] The following examples are given to illustrate the presentinvention, and are not intended to limit the scope of the invention. Theexamples utilize the L*a*b* or the L*C*h color space as described abovein order to evaluate color shifting properties of the coatings of thisinvention.

Example 1

[0152] Gold Pearl interference pigment was first washed in acetone anddried in an air oven. The dried pigment was then placed in a cooled dishplaced in a vacuum chamber pumped to a pressure of about 1 10⁻⁴ Torr andsubjected to DC magnetron coating of chromium in an Ar pressure of about2.5 10⁻³ Torr.

Example 2

[0153] Super Green Pearl pigment was similarly washed and dried asdescribed in Example 1. It too was exposed to sputter deposition ofchromium while being subjected to vibrational movement.

Example 3

[0154] Violet Pearl pigment was treated as described in Example 1. Itwas also sputter coated with chromium.

Example 4

[0155] Iriodin® 221 Blue pigment was coated with chromium in a barrelvacuum coater equipped with two chromium magnetron sources measuring5×15″ in size. The magnetrons were run at about 3 A at 3 mTorr Ar forbetween 6 and 20 min depending on the color enhancement required. A massof about 25-50 g of powder was processed without any pre-treatment,washing or drying.

Example 5

[0156] 289 Flash Interference Blue pigment was coated with Cr by thesame process as described in Example 4.

Example 6

[0157] 299 Flash Interference Green pigment was coated with Cr by thesame process as described in Example 4.

Example 7

[0158] Super Red Mearlin® Luster pigment was coated with Cr by the sameprocess as described in Example 4.

Example 8

[0159] The pigments identified in Examples 1-7 were utilized with noadditional coating as control pigments. Cr-coated pigments according toExamples 1-7 and the control pigments were sprayed onto white and ontoblack coated paper panels to produce test samples. The sprayed materialsincluded 25% by weight of pigment loading in an acrylic-melamine binder.The dried sprayed material was about 1 mil thick. The microscopiccharacteristics and colors of the control and Cr-coated samples arediscussed below.

Structural Characteristics

[0160] FIGS. 6A-6B, and 7A-7C show scanning electron microscopicpictures of sprayed control pigments and Cr-coated pigments according tothis invention. FIGS. 6A and 7A show scanning electron microscopicpictures of the surfaces of control Gold Pearl pigment at 50000× andcontrol Super Green Pearl pigment at 75000×, respectively. FIGS. 6B and7B show, respectively, scanning electron microscopic pictures of thesurface at 50000× of the chromium-coated Gold Pearl pigment in Example1, and of the surface at 75000× of the chromium-coated Super Green Pearlin Example 2. In addition, FIG. 7C shows a scanning electron microscopicpicture of the surface at 100000× of Super Green Pearl pigment that wascoated with Cr as described in Example 2.

[0161] Comparison of the picture shown in FIG. 6A with that shown inFIG. 6B reveals that the coating with Cr according to this invention hassimply replicated the underlying structure of the TiO₂ at 50000×magnification. Similarly, comparison of the picture shown in FIG. 7Awith that shown in FIG. 7B reveals that, even at the 75000×magnification level, the coating with Cr according to this invention hassimply replicated the underlying structure of the TiO₂. FIG. 7C showsthat no islands or rod-like particles of Cr are visible at the 100000×magnification level of the Cr-coated pigment according to thisinvention. Instead, the structure at this level of magnification stillappears as that of the underlying TiO₂ layer. Thus, a snow-ballstructure of TiO₂ clusters is observed in all the scanning electronmicroscopy pictures of the control and Cr-coated pigments according tothis invention.

[0162] In contrast, the photograph shown in U.S. Pat. No. 5,116,664 (the“'664 patent”), where the metal has been deposited by electrolessmethods, reveals the existence of finely divided rod-like particles (seealso col. 6, line 16 in the '664 patent). The magnification at which thephotograph in the '664 patent is shown is 72000×, whereas not even thephotograph shown in FIG. 7C, taken at 100000×, for the Cr-coated pigmentaccording to this invention shows the presence of any type of formationother than the uniform coating of the TiO₂ layer. In particular, noscanning electron microscopic picture of the chromium-coated surfaceaccording to this invention shows any rod-like formation or island.Instead, the pictures in FIGS. 6B, 7B, and 7C show a smooth replicationof the structure of the TiO₂ layer by the coating of chromium.

Optical Properties

[0163] Compared to the control samples, the chromium coated pigments insome samples exhibited a higher chroma, a higher dynamic color shift,and a higher hiding power. Hue changes, i.e., color changes, were alsonoted.

[0164] The higher hiding power was readily seen by comparing spray outsamples on white paper panels. Under visual inspection, the controlsamples on the white paper background showed a slight reflection incolor at near normal angle, but at a glancing angle the white paper wasreadily visible. On black paper, the control showed little difference inreflection at normal versus glancing angle, i.e., the colors werepractically the same. In contrast, the chromium-coated pigment showedlittle, if any, difference in color whether it was sprayed over a blackor white background. The pigment itself was also notably different. Thecontrol pigment was whitish in color whereas the Cr-coated pigment wascolored.

[0165] Upon visual inspection, the control samples on a white backgroundonly showed corresponding values for the control samples by a factor inthe range of approximately 1.4-2.6. This means that the available colorgamut for the Cr-coated pigments has been increased by the same factor.As shown in Table 1, the DCA™ value for the Violet Pearl+Cr on a blackbackground is lower than the corresponding value for the uncoated VioletPearl (control). This observation is explained in terms of an excess ofdeposited chromium, which results in lower chroma because it moves thecolor saturation towards the achromatic point at (a*, b*)=(0, 0), theorigin. This lower chroma decreases the DCA™ value. The chroma for theViolet Pearl+Cr is still higher than the chroma for the control with nochromium on the white background because the chroma for the control on awhite background is initially very low. Generally, as chromium is beingadded, the chroma and DCA™ values will increase, but with additionalchromium deposition the chroma and DCA™ values will ultimately decreaseas the pigment behaves more like chromium powder. The intensification ofchroma with the added layer of chromium is due to an increase inabsorption and interference effects.

Example 9

[0166] Further color characterization using D₆₅ illumination wasperformed with a Zeiss spectrophotometer to show the color at variousviewing angles; the measurements were also taken just off-glossconditions. FIG. 8 is a plot in a*b* color space that shows the hue andchroma changes for the three DuPont pigments in Examples 1-3 as theviewing angles change. For all the pigments whose chroma and hue areplotted in FIG. 8, the Cr-coated pigment as sprayed with the binder onwhite background has higher chroma than the corresponding control sampleas similarly sprayed with the binder on reflected color at near normalincidence. At higher angles, only the mass tone of the white backgroundis seen. In contrast, the treated Cr-coated interference mica showed thecolor of the pigment at all angles. This observation implies a muchimproved hiding power (hiding the background color) over the controlsamples.

[0167] Table 1 shows the difference between the color parameters for thecontrol pigments on white and on black paper panels versus the Cr-coatedpigments also on white and on black paper panels for the samples inExamples 1-3. The L*a*b* coordinates were measured at 10° incidence witha D₆₅ illuminant (CIE illuminant with a color temperature of 6504 K)with a Data Color 600 color integrating measuring instrument. DCA™calculations were based on color measurements using off-gloss (i.e.,specular) geometry on a Zeiss GK 311 M spectrophotometer. As describedhereinabove, DCA™ is a measure of the color gamut available as the angleof viewing is changed. TABLE 1 Color Properties of Coated and Un-CoatedInterference Mica Back- Sample ground DCA L* a* b* C* h Gold Pearl White49.4 90.6 −2.3 15.2 15.4 98.6 Gold Pearl + White 128.9 71.0 1.4 21.321.3 86.0 Cr Gold Pearl Black 89.1 76.8 −1.0 24.6 24.9 92.2 Gold Pearl +Black 130.9 66.5 1.72 25.5 25.6 86.2 Cr Super Green White 223.8 89.2−5.17 13.3 14.3 111.2 Super Green + White 487.3 67.7 −11.8 14.6 18.8129.0 Cr Super Green Black 380.6 75.1 −15.3 10.0 18.25 146.8 SuperGreen + Black 534.9 65.1 −14.7 15.0 21.0 134.5 Cr Violet Pearl White232.2 91.4 −0.77 5.74 5.79 97.7 Violet Pearl + White 523.8 50.9 8.1−16.0 17.9 296.6 Cr Violet Pearl Black 982.5 47.5 20.0 −27.7 34.2 305.8Violet Pearl + Black 716.9 43.9 10.7 −24.0 26.3 294.1 Cr

[0168] The DCA™ values in Table 1 for the Cr-coated pigments are greaterthan the white background. This is shown in FIG. 8 by the location ofthe chroma point loci for the Cr-coated pigments and those for thecorresponding control samples. The chroma point loci for the Cr-coatedpigments are farther from the center of the a*b* axis system than pointloci for the corresponding control samples. This is also satisfied forthe chroma point loci when the background is black for the pigments inExamples 1 and 2.

[0169] More specifically, the loci of chroma points 802 and 804 in FIG.8 correspond to the Gold Pearl interference pigment in Example 1 onwhite background in the form of control sample and with Cr-coatingaccording to this invention, respectively. Similarly, the loci of chromapoints 812, 814 and 822, 824 correspond to the pigments Super GreenPearl in Example 2 and Violet Pearl in Example 3, respectively. The loci812 and 822 are for the control samples on a white background and theloci 814 and 824 are for the Cr-coated pigments also on whitebackground. The pair of loci chroma points 812, 814 is for the pigmentin Example 2 and the pair of chroma points 822, 824 is for the pigmentin Example 3. The sets of loci of chroma points 804, 814 and 824 for theCr-coated pigments on white background are farther from the origin ofthe a*b* coordinate system than the respective counterparts 802, 812 and822 for the control samples on white background. In addition, the setsof loci of chroma points 803 and 813 for the Cr-coated pigments on blackbackground in Examples 1 and 2 are also farther from the origin of thea*b* coordinate system than the respective counterparts 801 and 811 forthe control samples on black background. These observations areconsistent with the changes in chroma values (C* values) given in Table1 for one measurement at 10°.

Example 10

[0170] Color measurements of the spray out paper panels were made onboth the white and black backgrounds for both Cr-coated and controlTiO₂-coated interference mica with a Zeiss color measuring instrumentset-up for multi-angle geometry. Data obtained with these measurementsare given in Tables 2-29. Samples were illuminated at 45° and 130°(second column in each one of Tables 2-29), and measured at five anglesrelative to the gloss angle using D₆₅ illumination. These angles were15°, 25°, 45°, 65° and 105° (given in the fourth column in each one ofTables 2-29), and numbered with ordinal numbers in the first column ofeach one of Tables 2-29. The entries in each of the second columns inthese tables are the angles of illumination. For each angle ofillumination, the angle of detection is listed in the third column underthe heading “View”. The gloss angle is the angle for which the angle ofincidence is equal to the angle of reflection, and the differencebetween the gloss angle and the angle of detection is the angle listedin the fourth column under the heading “Diff.” for each measurement. Thefifth column in each table under the heading “Filt.” provides theneutral density filter setting, where unity means that no filter wasused. These Tables provide numerical values for the CIE colorcoordinates a*, b*, L*, C*, and h for the different control andCr-coated pigments on white and on black backgrounds. TABLE 2 Sample:Control Violet Pearl in Example 3 on white background. Points (a*, b*)in this Table correspond to filled diamonds in FIG. 9. N Illum ViewDiff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 64.04 71.43 58.18 87.69−8.25 15.71 17.75 117.71 2 45 70 65 1 64.74 72.07 56.27 88.00 −8.0018.05 19.74 113.91 3 45 90 45 1 69.25 75.39 63.20 89.57 −4.77 14.4015.17 108.33 4 45 110 25 1 90.05 90.29 101.01 96.12 8.22 −2.68 8.65341.93 5 45 120 15 1 112.77 105.66 141.13 102.15 20.51 −15.40 25.65323.11

[0171] TABLE 3 Sample: Control Violet Pearl in Example 3 on blackbackground. Points (a*, b*) in this Table correspond to triangles inFIG. 9. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 15.41 5.22 8.73 27.36 5.60 −11.88 13.13 295.21 2 45 70 65 1 6.05 5.5610.54 28.28 8.91 −15.92 18.25 299.22 3 45 90 45 1 10.30 8.73 18.60 35.4616.77 −22.79 28.30 306.34 4 45 110 25 1 31.63 23.70 57.78 55.79 37.34−38.93 53.94 313.81 5 45 120 15 1 57.92 41.42 103.57 70.47 51.57 −48.5570.83 316.72

[0172] TABLE 4 Sample: Cr-coated Violet Pearl in Example 3 on whitebackground. Points (a*, b*) in this Table correspond to filled squaresin FIG. 9. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 16.68 6.96 6.23 31.71 0.83 4.83 4.90 80.29 2 45 70 65 1 8.31 8.58 8.6335.17 1.58 1.92 2.49 50.49 3 45 90 45 1 11.62 11.41 15.43 40.26 5.85−7.78 9.74 306.95 4 45 110 25 1 27.63 24.64 47.96 56.72 18.05 −27.5232.91 303.26 5 45 120 15 1 48.76 41.67 89.97 70.65 27.12 −39.18 47.65304.69

[0173] TABLE 5 Sample: Cr-coated Violet Pearl in Example 3 on blackbackground. Points (a*, b*) in this Table correspond to crosses in FIG.9. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 1.711.65 2.94 13.55 3.65 −9.35 10.03 291.30 2 45 70 65 1 2.72 2.56 5.0618.17 5.82 −13.31 14.53 293.62 3 45 90 45 1 5.90 5.37 11.55 27.76 9.54−19.69 21.88 295.86 4 45 110 25 1 23.08 19.44 46.98 51.20 22.53 −35.9942.46 302.05 5 45 120 15 1 47.23 38.27 96.72 68.22 33.35 −47.97 58.42304.81

[0174] TABLE 6 Sample: Control Gold Pearl in Example 1 on whitebackground. Points (a*, b*) in this Table correspond to filled diamondsin FIG. 10. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −1051 46.49 49.82 49.52 75.96 −2.09 4.02 4.53 117.46 2 45 70 65 1 45.4748.94 50.70 75.41 −2.64 1.85 3.22 144.94 3 45 90 45 1 57.64 61.87 57.0382.84 −2.47 8.43 8.79 106.31 4 45 110 25 1 114.22 122.06 83.71 107.97−2.33 29.65 29.74 94.49 5 45 120 15 1 180.92 192.41 113.90 128.28 −1.7144.76 44.80 92.19

[0175] TABLE 7 Sample: Control Gold Pearl in Example 1 on blackbackground. Points (a*, b*) in this Table correspond to triangles inFIG. 10. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 117.60 18.91 17.36 50.59 −1.77 5.84 6.10 106.86 2 45 70 65 1 21.13 22.5918.50 54.65 −1.37 10.51 10.60 97.43 3 45 90 45 1 35.80 38.10 25.57 68.09−1.08 21.01 21.03 92.94 4 45 110 25 1 90.79 96.71 51.95 98.71 −1.6240.76 40.79 92.27 5 45 120 15 1 145.09 154.20 77.74 118.02 −1.47 51.4551.47 91.63

[0176] TABLE 8 Sample: Cr-coated Gold Pearl in Example 1 on whitebackground. Points (a*, b*) in this Table correspond to squares in FIG.10. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 11.7412.28 12.56 41.66 0.67 1.59 1.73 67.04 2 45 70 65 1 13.93 14.60 14.0545.08 0.59 3.75 3.80 81.12 3 45 90 45 1 22.76 23.83 18.35 55.91 0.7712.99 13.01 86.60 4 45 110 25 1 70.08 73.27 40.14 88.58 1.31 36.22 36.2487.92 5 45 120 15 1 138.59 144.49 70.70 115.14 2.19 52.09 52.14 87.59

[0177] TABLE 9 Sample: Cr-coated Gold Pearl in Example 1 on blackbackground. Points (a*, b*) in this Table correspond to crosses in FIG.10. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 5.525.81 5.63 28.92 0.22 2.59 2.60 85.07 2 45 70 65 1 8.28 8.65 6.83 35.300.76 8.61 8.64 84.97 3 45 90 45 1 17.33 18.06 11.24 49.57 1.13 18.7918.83 86.57 4 45 110 25 1 65.89 68.77 34.08 86.39 1.56 40.09 40.12 87.775 45 120 15 1 136.62 142.66 65.35 114.59 1.89 55.64 55.67 88.06

[0178] TABLE 10 Sample: Control Super Green Pearl in Example 2 on whitebackground. Points (a*, b*) in this Table correspond to filled diamondsin FIG. 11. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −1051 51.50 53.66 44.77 78.27 1.65 13.10 13.20 82.81 2 45 70 65 1 50.8752.89 45.79 77.81 1.93 11.18 11.35 80.21 3 45 90 45 1 61.31 65.59 55.3784.79 −2.05 13.37 13.53 98.71 4 45 110 25 1 96087 109.82 90.76 103.68−12.26 17.22 21.14 125.44 5 45 120 15 1 126.91 148.45 126.98 116.33−19.33 16.63 25.50 139.31

[0179] TABLE 11 Sample: Control Super Green Pearl in Example 2 on blackbackground. Points (a*, b*) in this Table correspond to triangles inFIG. 11. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 116.33 19.30 21.82 51.03 −10.71 −2.03 10.90 190.73 2 45 70 65 1 20.1723.69 23.53 55.78 −10.91 3.16 11.36 163.82 3 45 90 45 1 31.55 37.4233.25 67.59 −13.80 8.80 16.37 147.49 4 45 110 25 1 68.29 83.30 71.0893.14 −22.26 13.86 26.22 148.10 5 45 120 15 1 100.44 124.95 110.37108.94 −28.83 13.55 31.85 154.83

[0180] TABLE 12 Sample: Cr-coated Super Green Pearl in Example 2 onwhite background. Points (a*, b*) in this Table correspond to squares inFIG. 11. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 18.83 9.35 8.78 36.65 −0.32 3.96 3.97 94.67 2 45 70 65 1 11.65 12.6410.99 42.21 −2.34 6.80 7.19 109.03 3 45 90 45 1 19.40 22.09 17.22 54.12−7.61 12.22 14.39 121.90 4 45 110 25 1 53.75 65.16 49.14 84.57 −19.6519.25 27.51 135.59 5 45 120 15 1 94.25 117.89 93.15 106.54 −29.17 20.5135.66 144.89

[0181] TABLE 13 Sample: Cr-coated Super Green Pearl in Example 2 onblack background. Points (a*, b*) in this Table correspond to crosses inFIG. 11. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 14.70 5.54 5.85 28.21 −6.85 0.42 6.87 176.51 2 45 70 65 1 7.68 9.10 7.8436.17 −8.54 6.37 10.65 143.30 3 45 90 45 1 15.60 18.66 14.25 50.28−11.70 12.26 16.95 133.65 4 45 110 25 1 49.73 61.69 46.12 82.75 −22.4319.35 29.62 139.22 5 45 120 15 1 87.73 110.80 87.67 104.04 −30.16 20.0136.19 146.44

[0182] TABLE 14 Sample: Control Super Red Merlin Luster in Example 7 onwhite background. Points (a*, b*) in this Table correspond to filleddiamonds in FIG. 12. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 4570 65 1 58.75 67.62 59.57 85.82 −12.58 11.19 16.84 138.35 2 45 90 45 167.88 75.06 66.88 89.42 −7.11 10.94 13.05 123.02 3 45 110 25 1 110.03107.50 101.56 102.83 13.25 8.54 15.76 32.80 4 45 120 15 1 161.72 147.23139.02 115.96 28.60 9.52 30.14 18.41 5 130 155 −105 1 57.08 64.28 58.8384.11 −9.32 8.93 12.91 136.21

[0183] TABLE 15 Sample: Control Super Red Merlin Luster in Example 7 onblack background. Points (a*, b*) in this Table correspond to squares inFIG. 12. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 1 13.3212.39 14.23 41.83 10.66 −2.27 10.90 347.99 2 45 90 45 1 21.45 18.7621.45 50.41 18.45 −2.43 18.60 352.49 3 45 110 25 1 56.05 46.02 48.5573.56 33.63 0.88 33.64 1.50 4 45 120 15 1 93.99 76.13 74.93 89.92 42.015.20 42.33 7.06 5 130 155 −105 1 12.41 12.19 12.89 41.51 5.98 0.49 6.004.69

[0184] TABLE 16 Sample: Cr-coated Super Red Merlin Luster in Example 7on white background. Points (a*, b*) in this Table correspond totriangles in FIG. 12. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 4570 65 1 8.98 8.32 9.56 34.63 9.66 −2.02 9.87 348.19 2 45 90 45 1 17.4915.40 17.76 46.18 16.61 −2.58 16.81 351.17 3 45 110 25 1 48.18 40.9843.30 70.16 27.61 0.78 27.63 1.61 4 45 120 15 1 77.12 65.35 65.13 84.6632.84 4.24 33.11 7.35 5 130 155 −105 1 5.26 5.18 5.63 27.25 4.32 0.304.34 355.98

[0185] TABLE 17 Sample: Cr-coated Super Red Merlin Luster in Example 7on black background. Points (a*, b*) in this Table correspond to crossesin FIG. 12. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 17.38 6.83 8.07 31.41 9.15 −2.68 9.53 343.70 2 45 90 45 1 14.03 12.4114.25 41.86 15.07 −2.26 15.24 351.47 3 45 110 25 1 39.74 33.77 36.3864.78 26.01 −0.17 26.01 359.63 4 45 120 15 1 69.38 58.53 59.11 81.0332.32 3.36 32.49 5.94 5 130 155 −105 1 5.21 5.00 5.67 26.72 5.90 −1.406.06 346.65

[0186] TABLE 18 Sample: Control Merck Iriodin ® 221 Blue in Example 4 onwhite background. Points (a*, b*) in this Table correspond to filleddiamonds in FIG. 13. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 4570 65 1 69.83 72.82 54.97 88.36 1.70 19.92 20.00 85.11 2 45 90 45 175.52 79.43 70.94 91.43 0.44 11.01 11.02 87.70 3 45 110 25 1 88.45 94.28112.60 97.75 −1.71 −7.10 7.31 256.43 4 45 120 15 1 95.35 101.31 137.08100.50 −1.23 −16.12 16.16 265.64 5 130 155 −105 1 63.75 67.23 49.5785.62 0.02 20.62 20.62 89.95

[0187] TABLE 19 Sample: Control Merck Iriodin ® 221 Blue in Example 4 onblack background. Points (a*, b*) in this Table correspond to squares inFIG. 13. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 1 18.5920.53 32.40 52.43 −4.48 −16.17 16.78 254.52 2 45 90 45 1 22.40 25.2842.96 57.35 −7.04 −20.93 22.08 251.40 3 45 110 25 1 35.00 39.58 81.0969.17 −8.44 −35.30 36.30 256.56 4 45 120 15 1 45.35 50.24 115.12 76.22−6.46 −45.72 46.18 261.96 5 130 155 −105 1 19.02 20.31 30.82 52.19 −1.20−14.38 14.43 265.24

[0188] TABLE 20 Sample: Cr-coated Merck Iriodin ® 221 Blue in Example 4on white background. Points (a*, b*) in this Table correspond totriangles in FIG. 13. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 4570 65 1 9.23 9.95 14.17 37.74 −1.64 −9.17 9.31 259.84 2 45 90 45 1 14.1915.64 25.72 46.50 −3.94 −16.46 16.92 256.54 3 45 110 25 1 30.97 33.9871.26 64.94 −4.56 −34.91 35.21 262.56 4 45 120 15 1 45.84 49.26 113.8075.61 −2.45 −45.99 46.05 266.95 5 130 155 −105 1 7.37 7.69 10.48 33.340.72 −7.04 7.08 275.83

[0189] TABLE 21 Sample: Cr-coated Merck Iriodin ® 221 Blue in Example 4on black background. Points (a*, b*) in this Table correspond to crossesin FIG. 13. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 17.49 8.31 13.71 34.63 −3.67 −13.43 13.92 254.71 2 45 90 45 1 11.94 13.4224.41 43.38 −5.36 −19.68 20.40 254.76 3 45 110 25 1 27.05 29.99 64.5161.64 −5.49 −34.91 35.34 261.06 4 45 120 15 1 40.30 43.59 102.10 71.95−3.16 −45.05 45.16 265.99 5 130 155 −105 1 6.05 6.44 10.29 30.49 −0.62−11.36 11.38 266.85

[0190] TABLE 22 Sample: Control Iriodin ® Flash Interference Blue inExample 5 on white background. Points (a*, b*) in this Table correspondto filled diamonds in FIG. 14. N Illum View Diff. Filt. X Y Z L* a* b*C* h 1 45 70 65 1 64.02 65.80 47.85 84.90 3.77 21.18 21.51 79.91 2 45 9045 1 68.11 70.52 56.17 87.25 2.75 16.85 17.08 80.73 3 45 110 25 1 90.2097.93 110.29 99.19 −4.77 −3.21 5.75 213.93 4 45 120 15 1 128.74 143.80222.82 114.93 −10.68 −29.39 31.27 250.02 5 130 155 −105 1 63.93 67.2250.28 85.61 0.46 19.87 19.88 88.68

[0191] TABLE 23 Sample: Control Iriodin ® Flash Interference Blue inExample 5 on black background. Points (a*, b*) in this Table correspondto squares in FIG. 14. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 4570 65 1 12.32 13.40 22.27 43.36 −2.63 −16.06 16.27 260.68 2 45 90 45 115.89 17.80 29.89 49.25 −5.58 −18.10 18.94 252.88 3 45 110 25 1 34.8841.12 76.30 70.26 −13.54 −29.76 32.70 245.53 4 45 120 15 1 70.68 83.41179.34 93.19 −17.29 −49.06 52.01 250.58 5 130 155 −105 1 12.61 13.3322.61 43.26 −0.24 −16.81 16.82 269.17

[0192] TABLE 24 Sample: Cr-coated Iriodin ® Flash Interference Blue inExample 5 on white background. Points (a*, b*) in this Table correspondto triangles in FIG. 14. N Illum View Diff. Filt. X Y Z L* a* b* C* h 145 70 65 1 5.30 5.70 8.42 28.64 −1.20 −8.64 8.72 262.12 2 45 90 45 18.93 9.88 15.17 37.62 −3.64 −11.73 12.28 252.75 3 45 110 25 1 29.1632.78 55.52 63.98 −7.23 −22.64 23.77 252.28 4 45 120 15 1 70.04 77.93144.18 90.75 −8.14 −36.62 37.51 257.47 5 130 155 −105 1 3.58 3.73 5.5122.75 −0.65 −7.50 7.53 274.96

[0193] TABLE 25 Sample: Cr-coated Iriodin ® Flash Interference Blue inExample 5 on black background. Points (a*, b*) in this Table correspondto crosses in FIG. 14. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 4570 65 1 4.54 4.94 7.85 26.58 −1.95 −10.22 10.40 259.17 2 45 90 45 1 7.728.59 13.73 35.18 −3.92 −12.52 13.12 252.61 3 45 110 25 1 23.37 26.2244.38 58.24 −6.52 −20.98 21.97 252.75 4 45 120 15 1 52.35 58.40 105.9680.96 −7.75 −31.96 32.89 256.37 5 130 155 −105 1 3.31 3.49 5.81 21.890.02 −10.31 10.31 270.13

[0194] TABLE 26 Sample: Control Iriodin ® Flash Interference Green inExample 6 on white background. Points (a*, b*) in this Table correspondto filled diamonds in FIG. 15. N Illum View Diff. Filt. X Y Z L* a* b*C* h 1 45 70 65 1 66.46 68.11 69.73 86.06 4.23 2.75 5.05 33.02 2 45 9045 1 69.38 71.66 72.99 87.81 3.12 3.11 4.40 44.86 3 45 110 25 1 92.14100.31 93.32 100.12 −5.26 9.32 10.70 119.43 4 45 120 15 1 154.64 180.40150.44 125.21 −20.11 19.65 28.12 135.66 5 130 155 −105 1 67.48 69.7567.54 86.88 2.98 5.99 6.70 63.55

[0195] TABLE 27 Sample: Control Iriodin ® Flash Interference Green inExample 6 on black background. Points (a*, b*) in this Table correspondto squares in FIG. 15. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 4570 65 1 6.45 7.17 11.38 32.18 −3.53 −11.59 12.11 253.06 2 45 90 45 110.59 12.35 15.21 41.76 −8.15 −4.69 9.40 209.90 3 45 110 25 1 37.5346.25 39.58 73.71 −19.55 11.24 22.55 150.10 4 45 120 15 1 87.38 109.7185.80 103.64 −29.10 20.66 35.69 144.63 5 130 155 −105 1 5.46 5.98 10.5329.35 −2.40 −14.04 14.24 260.28

[0196] TABLE 28 Sample: Cr-coated Iriodin ® Flash Interference Green inExample 6 on white background. Points (a*, b*) in this Table correspondto triangles in FIG. 15. N Illum View Diff. Filt. X Y Z L* a* b* C* h 145 70 65 1 8.36 8.97 11.32 35.94 −1.29 −4.95 5.12 255.42 2 45 90 45 112.86 14.25 15.29 44.60 −4.26 0.03 4.26 179.57 3 45 110 25 1 41.41 48.4238.96 75.09 −13.26 14.38 19.56 132.67 4 45 120 15 1 112.72 136.54 101.05112.69 −25.01 25.86 35.98 134.04 5 130 155 −105 1 6.79 7.24 9.85 32.35−0.80 −6.84 6.89 263.36

[0197] TABLE 29 Sample: Cr-coated Iriodin ® Flash Interference Green inExample 6 on black background. Points (a*, b*) in this Table correspondto crosses in FIG. 15. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 4570 65 1 6.87 7.58 10.27 33.09 −3.11 −6.85 7.52 245.57 2 45 90 45 1 10.6212.01 13.60 41.24 −5.65 −1.76 5.92 197.29 3 45 110 25 1 32.85 38.6532.04 68.50 −13.03 12.03 17.73 137.30 4 45 120 15 1 84.12 101.35 76.18100.52 −21.78 22.50 31.32 134.07 5 130 155 −105 1 5.59 6.13 9.24 29.74−2.61 −9.44 9.79 254.53

[0198] FIGS. 9-15 show the plots of the data given in Tables 2-29 forthe respective pigments: Violet Pearl, Gold Pearl, Super Green Pearl,Super Red Mearlin Luster, Merck Iriodin® 221 Blue, Iriodin®289 FlashInterference Blue, and Iriodin® 299 Flash Interference Green. The colorcharacteristics are plotted in the a*b* space for the correspondingcontrol sample on white and on black backgrounds and for the Cr-coatedpigment according to this invention on white and on black backgrounds.

[0199] FIGS. 9-15 invariably show in all cases that the Cr-coatedpigments according to this invention gave nearly the same colortrajectory on both the white and black backgrounds whereas the controlsamples gave widely different color trajectories. This means that theCr-coated pigments according to this invention will give paints a moreconstant color when painted over varying colored backgrounds. One of thepractical consequences of this new attribute is that it allows a paintshop more freedom in repairs, especially when the paint is coveringdifferent colored bases.

[0200] The present invention may be embodied in other specific formswithout departing from its spirit or essential characteristics. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescribed. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

1. A method of forming a pigment composition, comprising: placing aninorganic powdered substrate material in a vacuum chamber containing oneor more coating material vaporization sources; generating a coatingmaterial vapor from the one or more coating material vaporizationsources in a dry vacuum process; exposing the powdered substratematerial to the coating material vapor in a substantially uniformmanner; and forming a coalescence film of one or more layers of coatingmaterial on the powdered substrate material that substantiallyreplicates a surface microstructure of the powdered substrate material.2. The method of claim 1, wherein the powdered substrate materialcomprises a silicatic material.
 3. The method of claim 1, wherein thepowdered substrate material is selected from the group consisting ofmica flakes, glass flakes, talc, boron nitride, and combinationsthereof.
 4. The method of claim 1, wherein the powdered substratematerial comprises a silicatic material precoated with a high refractiveindex dielectric material.
 5. The method of claim 4, wherein the highrefractive index dielectric material is selected from the groupconsisting of titanium dioxide, zirconium oxide, tin oxide, iron oxide,zinc oxide, tantalum pentoxide, magnesium oxide, tungsten trioxide,carbon, and combinations thereof.
 6. The method of claim 1, wherein thepowdered substrate material comprises a TiO₂-coated interference mica.7. The method of claim 1, wherein the coating material is a lightabsorbing material.
 8. The method of claim 1, wherein the coatingmaterial is selected from the group consisting of metals, oxides,sub-oxides, nitrides, oxynitrides, borides, sulfides, carbides, andcombinations thereof.
 9. The method of claim 1, wherein the coatingmaterial comprises an absorber material selected from the groupconsisting of chromium, titanium, palladium, tin, aluminum, silicon,carbon, copper, cobalt, nickel, titanium silicide, hastelloys, monels,inconels, nichromes, stainless steels, and combinations thereof.
 10. Themethod of claim 1, wherein the coalescence film has a thickness fromabout 30 Å to about 150 Å.
 11. The method of claim 1, wherein thecoating material vaporization sources are selected from the groupconsisting of evaporative sources, sputtering sources, electron beamdeposition sources, and arc vapor deposition sources.
 12. The method ofclaim 1, wherein the dry vacuum process is carried out at a temperatureof less than about 200° C.
 13. The method of claim 1, wherein the dryvacuum process is carried out at a temperature of about 200° C. orgreater.
 14. The method of claim 1, wherein the dry vacuum process iscarried out at a near ambient temperature.
 15. The method of claim 1,wherein the dry vacuum process comprises a physical vapor depositionprocess.
 16. A pigment composition, comprising: a powdered substratematerial comprising a plurality of inorganic core particles having anobservable surface microstructure; and a coalescence film of one or morelayers of a light absorbing material substantially surrounding the coreparticles of the substrate material, the coalescence film substantiallyreplicating the surface microstructure of the core particles.
 17. Thepigment composition of claim 16, wherein the powdered substrate materialcomprises a silicatic material.
 18. The pigment composition of claim 16,wherein the powdered substrate material is selected from the groupconsisting of mica flakes, glass flakes, talc, boron nitride, andcombinations thereof.
 19. The pigment composition of claim 16, whereinthe powdered substrate material comprises a silicatic material precoatedwith a high refractive index dielectric material.
 20. The pigmentcomposition of claim 19, wherein the high refractive index dielectricmaterial is selected from the group consisting of titanium dioxide,zirconium oxide, tin oxide, iron oxide, zinc oxide, tantalum pentoxide,magnesium oxide, tungsten trioxide, carbon, and combinations thereof.21. The pigment composition of claim 16, wherein the powdered substratematerial comprises a TiO₂-coated interference mica.
 22. The pigmentcomposition of claim 16, wherein the coalescence film comprises amaterial selected from the group consisting of metals, oxides,sub-oxides, nitrides, oxynitrides, borides, sulfides, carbides, andcombinations thereof.
 23. The pigment composition of claim 16, whereinthe coalescence film comprises a material selected from the groupconsisting of chromium, titanium, palladium, tin, aluminum, silicon,carbon, copper, cobalt, nickel, titanium silicide, hastelloys, monels,inconels, nichromes, stainless steels, and combinations thereof.
 24. Thepigment composition of claim 16, wherein the coalescence film has athickness from about 30 Å to about 150 Å.
 25. A pigment flake,comprising: an inorganic core particle having an observable surfacemicrostructure; and a coalescence film of one or more layers of a lightabsorbing material substantially surrounding the core particle, thecoalescence film substantially replicating the surface microstructure ofthe core particle.
 26. The pigment flake of claim 25, wherein theinorganic core particle comprises a silicatic material.
 27. The pigmentflake of claim 25, wherein the inorganic core particle comprises amaterial selected from the group consisting of mica flake, glass flake,talc, boron nitride, and combinations thereof.
 28. The pigment flake ofclaim 25, wherein the inorganic core particle comprises a silicaticmaterial precoated with a high refractive index dielectric material. 29.The pigment flake of claim 28, wherein the high refractive indexdielectric material is selected from the group consisting of titaniumdioxide, zirconium oxide, tin oxide, iron oxide, zinc oxide, tantalumpentoxide, magnesium oxide, tungsten trioxide, carbon, and combinationsthereof.
 30. The pigment flake of claim 25, wherein the inorganic coreparticle comprises a TiO₂-coated interference mica.
 31. The pigmentflake of claim 25, wherein the coalescence film comprises a materialselected from the group consisting of a metal, an oxide, a sub-oxide, anitride, an oxynitride, a boride, a sulfide, a carbide, and combinationsthereof.
 32. The pigment flake of claim 25, wherein the coalescence filmcomprises a material selected from the group consisting of chromium,titanium, palladium, tin, aluminum, silicon, carbon, copper, cobalt,nickel, titanium silicide, hastelloys, monels, inconels, nichromes,stainless steels, and combinations thereof.
 33. The pigment flake ofclaim 25, wherein the coalescence film comprises alternating layers oftwo different absorber materials.
 34. The pigment flake of claim 33,wherein the alternating layers of two different absorber materials areselected from the group consisting of Ti/C, Pd/C, Zr/C, Nb/C, Al/C,Cu/C, Ti/W, Ti/Nb, Ti/Si, Al/Si, Pd/Cu, Co/Ni, and Cr/Ni.
 35. A pigmentflake, comprising: a glass core particle having an observable surfacemicrostructure; and a coalescence film of one or more layers of a lightabsorbing material comprising aluminum substantially surrounding thecore particle, the coalescence film substantially replicating thesurface microstructure of the core particle.